The smallest military unit is called a cohort. A cohort is comprised of 1000 men; these 1000 men are subtracted from the manpower pool when the cohort is recruited. A number of cohorts can be grouped to form an army.
Cohorts are trained in cities at a cost of money, manpower and time. When a cohort is fully trained, an army is created to "house" it; or alternatively, the newly trained cohort will join an existing army if one is currently residing in the city, which the cohort is build.
Cohorts can usually be moved between Armies at any time for no cost.
All units types in Imperator: Rome have the same identical basic stats. These are:
- strength = All units start at 1000 strength, equivalent to the 1000 manpower it cost to build
- morale = 3.0
List of unit types
There are 10 types of land units. Only 2 (3 if you count Supply Trains) of them are always available. Others can be acquired by having required resources or Military Traditions.
|Unit type||Monthly upkeep||Build requirements||Siege assault||Movement
|Attrition weight||Attrition loss||Food storage||Food consumption|
|Archers||6||45||0.24||none, always available||✔||2.5||1||+25%||−10%||5%||2.4||0.1||−10%||−10%||+10%||−10%||+25%||+100%|
|Chariots||6||45||0.24||Military tradition: Barbarian or Indian||✘||2.5||1||5%||2.4||0.2||+20%||−10%||−50%||−10%||−50%||+10%||+35%||−50%||+100%|
|Horse Archers||14||60||0.58||Steppe Horses||✘||4||5||+25%||+50%||5%||3||0.25||+25%||−10%||+25%||−10%||+25%||−10%||+25%||−20%||+100%|
|Light Infantry||6||30||0.24||none, always available||✔||2.5||1||−25%||−50%||2.5%||2.4||0.1||−10%||−10%||−25%||−25%||−50%||−25%||+100%|
|Supply Train||16||120||0.66||none, always available||✘||2.5||1||+100%||10%||50||0.05||−90%||−90%||−90%||−90%||−90%||−90%||−90%||−90%||−90%|
- Siege assault: Whether this unit type can assault forts.
- Movement speed: Speed in the map.
- Maneuver: How many squares away this unit type can target enemies on the Battle chess board. All land units have at least 1 maneuver so they can target at least 3 squares.
- Morale damage taken: Affects how fast the unit flees from combat. Also affects caused morale damage (scales with unit's morale)
- Strength damage taken: Affects how much manpower will be lost in combat. Also slightly affects all caused damage (scales with unit's strength).
- Attrition weight: Modifies the size of a unit for the purpose of determining whether the army exceeds the supply limit of the city it's in. This does not affect how many units can be transported by sea.
- Unit type icons: Multiplier for caused damage against that unit type.
Modifiers to unit types
- Discipline: Increases caused damage.
- Terrain bonus: Increases caused damage when fighting in a specific terrain.
- Offense: Increases caused damage.
- Defense: Reduces received damage.
- Morale: Increases caused morale damage and makes the unit stay longer in combat.
- Maintenance: Reduces upkeep costs.
- Starting experience: Increases initial experience when recruiting this unit.
Each cohort may also become loyal to a specific character giving +10% Discipline.
Unit type strategy
Based on the various bonuses and penalties, each unit type seems to fall into certain categories.
These are not combat units. Their only ability is to have a lot of food capacity, in case attrition is a major issue. But they do still seem to count for calculations like Cohorts for sieges. When looking at unit's strengths, there is no point even including this one. It takes +100% and deals −90% damage towards everything. If it is deployed to the battle, you may need more units to put in the front line.
Their high price means they should be deployed in moderation, but their long time to fill up with food means they should not be deployed to late either.
There are only a few good things you can say about light infantry. While every other unit has some unit they counter, light infantry only has some units they are not too heavily countered by:
- They are cheap, with the same price Level as archers and chariots. They have a incredibly low attrition weight. Both this and the gold price makes them ideal if bodies rather then quality are needed, like for sieges. However even here, archers might to be better in all but the most extreme cases.
- They have a lot of buffs from trade goods (leather and base metals) and a fair share of military traditions.
- A decent amount of combat tactics also have a high efficiency for them.
- While they take −25% morale damage, that barely offsets them taking around +25% morale and strength damage from every enemy. That also means they churn through more manpower in battle than perhaps any other unit.
- They can be used to "pad out" the side of the front line, to avoid the enemy being able to fully use flanking. This is a rare case where the reduced morale damage could be useful, despite the cost in manpower.
- They also have a lot of damage penalties. Their only hope seems to be to outlast the enemy on the morale front. They could also outnumber the enemy on sheer cohort count 1:2 at comparable prices − except manpower of course.
- Dromedary cavalry are the only thing they can claim to counter somewhat.
The first step up from light infantry and a mainstay of many armies.
- Their increased morale damage makes them more likely to flee, but such a behaviour can conserve manpower and make room for the 2nd tier cohorts − ideally things countering whatever drove off the archers. They are supposed to deal damage, but fall back to let others deal damage if they are countered.
- They do very well against heavy infantry, at a fraction of the cost.
- Not a lot of combat tactics make good use of them.
- Heavy and light cavalry in turn counter them heavily, but again they can quickly disengage due to extra morale damage without taking too many losses.
Old technology from the Bronze Age, they are largely outdated by the time of the game and accordingly only used by few:
- Only available to barbarians and a few other military traditions.
- The poor man's heavy infantry. If you lack the resources or the supply for those but have them available, they are a viable alternative.
- Stronger vs archers, light infantry and light cavalry than heavy infantry; extra countered by heavy infantry and heavy cavalry. Cannot assault in a siege.
- Can deal a lot of damage, but also takes a lot.
- As cheap as light infantry and archers when available.
The mainstay of civilised and barbarian field armies of the period, but often hard to get:
- Requires Iron, a rather rare trade-good in some areas. Chariots are usually an alternative in those cases.
- They also cost a lot of supply and money, making them primarily useful in very favourable terrain with high civilisation.
- Archers and horse archers counter them, and of course elephants. Most other unit types have a poor match up.
The ultimate melee unit, with a very high price to match. In almost everything the antithesis of the light infantry:
- Extremely expensive in money, supply, food and even time
- The ultimate first line in the game
- They barely take any strength damage and deal a lot of damage in return
- Strategies that affect them tend to have more effect then on any other unit type, with Shock Action giving a unmatched 200%.
- One-on-one, there is no unit that has any hope of countering them.
- The only hope to beat them is to outnumber them. While fairly doable given its steep price, it is also quite costly in manpower.
- While cavalry does half damage, it also takes less than anyone else. Factoring in the effects of maneuver and price, they are the closest to a counter.
- Archers, heavy infantry and even light infantry could be a counter option if cavalry is lacking.
- Supply might be their worst enemy.
Coming out of the Bronze Age, riding horses became a major factor in warfare:
- Almost as cheap as archers and light infantry.
- Very high maneuver, with easily available horses. Usually the first flanking option one can find.
- Quite deadly against archers and the only counter to horse archers, making them a possible 1st Cohort option.
- Very good and very available flanker.
- Best movement speed in the game, making them useful for quick reaction forces.
The light cavalry of the desert regions.
- Use almost exactly like light cavalry: see there for the basics.
- More expensive in gold.
- Inferior combat bonuses, but also penalties.
- Comparatively good supply, food storage/consumption and high maneuver.
The result of putting armor on horses and riders is something totally different in use:
- Available once light cavalry is, but utterly different use case.
- Works nothing like any other cavalry units, more like a heavy infantry variant.
- Terrible maneuver. Not used for flanking, for the front line.
- More expensive in supplies and money.
- Stronger than heavy infantry against archers and most cavalry.
- The primary counter is heavy infantry, but horse archers are able to outlast them.
- Pretty good movement speed can give them a place in reaction forces.
Combines the best parts of cavalry and archers:
- In bonuses, penalties and stats, it uses the better of archers or light cavalry.
- In money and supply, it is the same as heavy infantry.
- Counters heavy infantry, but countered by light cavalry.
- The ultimate maneuver/flanking unit.
- Light cavalry is the only that deals good damage to them.
These are a special unit type, composed by Light infantry, available only to migratory tribes. Migratory units are created in the territory tab at the cost of 8 stability (this value can be modified by laws and by lowering centralization level). Migratory units can move across borders without military access and can settle in uncolonized lands or in occupied enemies' territories.
Migratory units, beyond settling, can perform two specific actions in non-owned colonized territories where they are standing:
- Raze: at the cost of +2 aggressive expansion, civilization in the territory will be reduced by half and the tribe gains advancement in each technology field equal to the amount of civilization razed divided by 10 (e.g. razing a 44 civilization territory will reduce civilization to 22 and give +2.22 technology advance in every field). The razed territory gets the Razed! modifier (−0.01% monthly civilization change) for five years.
- Pillage: Available only in territories with at least 20 civilization level. The tribe gets an amount of political influence and gold. The pillaged territory gets the Province Pillaged modifier (-0.25% local population growth, −25% commerce value) for five years.
If this actions are performed two times in a row against the same target the migratory tribes will automatically declare war against the province's owner with the Show Superiority casus belli.
Migratory units can be merged with regular units but can't be raised during war.